Ventilate the bathroom
Remove loose dirt and soap scum with warm water
Mix baking soda and water into a paste
Apply the paste to the grout
Spray or pour white vinegar over the paste
Let it fizz for a few minutes
Scrub the grout with a stiff brush or old toothbrush
Rinse thoroughly with warm water
Repeat on stubborn stains
Use hydrogen peroxide for tough discoloration
Avoid bleach on colored grout
Dry the grout with a clean towel
Apply grout sealer after cleaning if needed